Solid rocket propellant must be designed, evaluated and produced so as to evolve or generate hot gas in a controllable manner. This controlled evolvement of hot gas can then be utilized to propel a missile, rocket or other projectile in a predictable way.
It is well known to those skilled in the art that to ensure controlled gas evolution (burning), the following ballistic performance parameters of the propellant must be measured:
(1) burn rate (r) as a function of pressure, generally given by (r) in the equation r=aP.sup.n, where P is the pressure; PA1 (2) burn rate exponent, generally given by (n) in the same equation; PA1 (3) burn rate pre-factor, generally given by (a) in the same equation; PA1 (4) burn rate sensitivity to temperature given by ##EQU1## written as .sigma..sub.p ; and (5) pressure sensitivity with respect to area ratio where the area ratio is defined as K=propellant burning surface area divided by rocket nozzle throat area, where the pressure sensitivity is defined as: ##EQU2## PA1 (a) research and development programs where small (one to two gallon) quantities of new experimental propellants are formulated; PA1 (b) lot set evaluations where new lots of propellant ingredients are evaluated by making small (less than five gallons) mixes; and PA1 (c) surveillance programs where small (less than five inches in diameter) missiles are dismantled and propellant grain is removed for testing. In each of these situations there is insufficient propellant to test completely by the prior art methods described.
There are two methods presently used to measure the foregoing quantities. The first is called strand burning. Well-known to those skilled in the art is the Chemical Propulsion Information Agency(CPIA) handbook which contains standard data for strand burning of various propellants, some of which data is contained in graph form. This method consists of cutting the propellant into spaghetti size strands and then burning them at various constant temperatures and pressures. The strands must be burned in a costly device, a Crawford Bomb, which requires much maintenance. Additionally, many strands must be burned (requiring multiple test burns) to collect the data required to evaluate the aforementioned parameters (1) through (4). This procedure is very time consuming and expensive. Parameter (5) cannot be evaluated by the strand burning method.
Further, the foregoing known strand burning method does not allow testing of the propellant under the actual conditions inside a rocket motor. Although the strands are brought to the required pressure by external means, such as nitrogen pressure, and then ignited and burned, such environment does not simulate the turbulent conditions the propellant actually experiences inside a rocket motor.
The second known method uses a Ballistic Evaluation Motor (BEM). Such method has two advantages over strand burning. First, the BEM allows evaluation of all five parameters, not just (1) through (4). Secondly, the propellant can be evaluated in an environment that simulates conditions inside a rocket motor. Such simulation is not possible with strand burning.
There are several types of BEM's used by those familiar with propellant evolution technology. All types share the same disadvantages. They are expensive, time consuming to use and as in strand burning, they require large quantities of propellant.
There are many circumstances where large quantities of propellant are not available to test. These include: